小阳为了测量某金属块的密度，他找来一根均匀的直硬棒，用细线系_爱下问搜题

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问题实验题

小阳为了测量某金属块的密度，他找来一根均匀的直硬棒，用细线系在O点吊起，硬棒在水平位置平衡，然后将金属块B挂在硬棒左端C处，另外找一个重物A挂在硬棒右端，调节重物A的位置，使硬棒在水平位置平衡，此时重物A挂在硬棒上的位置为E，如图所示。下面是小阳测出金属块B密度的部分实验步骤，请你按小阳的思路，将实验步骤补充完整。

（1）用刻度尺测出OE的长度L₀。

（2）把金属块B浸没在水中，把重物A从E处移动到D处时，硬棒再次在水平位置平衡。

（3）。

（4）利用上述测量出的物理量和题中的已知量，计算B物体的密度的表达式是：ρ_B＝。(2分)

答案

用刻度尺测量出OD的长度L₁ ρ_B＝ρ_水L₀/(L₀－L₁)

题目分析：小阳的思路是利用杠杆平衡条件和水的密度来测量金属块的密度，金属块B在空中和浸没在水中时，重物A对对杠杆拉力的力臂是不同的，所以要分别测出两种情况下的力臂；设金属块B对杠杆拉力的力臂为L_B,金属块B在水中受到的浮力为F_浮，由杠杆平衡条件可知：G_B×L_B=G_A×L₀，（G_B-F_浮）×L_B=G_A×L₁，则有G_B/（G_B-F_浮）=L₀/L₁,整理得：G_B/F_浮=L₀/（L₀-L₁),又因为金属块B浸没在水中，V物=V排，所以ρ_B/ρ_水=L₀/（L₀-L₁)，即ρ_B＝ρ_水L₀/(L₀－L₁)。

多项选择题案例分析题

患儿女，6岁，16kg。因右肾挫裂伤5天，保守治疗后发热伴尿少2天，全麻下行右肾切除术后即出现氧饱和度降低。查体：BP120/80mmHg，HR140次/分，机械通气FiO₂0.8，SpO₂90%。唇稍发绀，心音强，P^3-亢进，双肺呼吸音粗，双下肺少许湿啰音，体温38.7℃。

明确低氧血症的原因，进一步的检查措施包括（）

A.动脉血气监测

B.中心静脉压监测

C.尿量监测

D.心肌酶学

E.胸部X线片

F.血淀粉酶

完形填空

A little boy was spending his Saturday morning playing in his sandbox. While creating roads in the soft sand, he   36  a large rock in the middle of the sandbox.
The boy   37  around the rock, managing to move it out from the dirt. With much   38 , he tried to push the rock out of the sandbox. When the boy got the rock to the edge(边缘) of the sandbox,   39 , he found that he couldn’t   40  it up and over the little wall. The rock was too   41  for his small body.
As he   42  to accept his failure, the little boy dug, pushed, and pried(撬动), but every time he thought he had made some   43 , the rock rolled and then fell back into the sandbox. The little boy   44  again and again, but the only   45  was to have the rock roll back.
46 , he burst into tears. All this time the boy’s father   47  him from his living room. The moment the tears fell, a   48  voice rose above the boy’s head. It was his father. 49 , but firmly(坚定地) he said, “Son, why didn’t you use all the   50  that you had? The boy replied with tears, “But I did, Daddy, I did! I   51  all that I had!” “No, son, you didn’t,” 52  the father kindly. “You didn’t   53  me to help you.” With that the father picked up the rock and   54  it out of the sandbox.
Are you discovering that you don’t have the strength to move your “rocks” away? There is ONE who is always willing to   55  you with the strength you need. We also need that strength, especially in our daily life.